Allosteric Regulation of Soluble Guanylyl Cyclase: The Nitric Oxide Receptor

Abstract

Nitric oxide (NO) signaling regulates numerous physiological processes, including vascular tone, memory formation, wound healing, sexual arousal, digestion, and renal filtration. Soluble guanylyl/guanylate cyclase (sGC) is the primary NO receptor, and functions by synthesizing cyclic guanosine-3',5'-monophosphate (cGMP) in response to sub-nanomolar levels of NO. Impaired sGC function is implicated in nearly all forms of cardiovascular disease, and small molecule stimulators of sGC represent a promising opportunity to treat vascular dysfunction. Despite recent clinical success, pharmacological development of sGC stimulators is limited by a lack of understanding as to where these compounds bind and how they function. This work describes the localization of stimulator binding to a conserved pocket in the heme domain of sGC, as well as bacterial homologues, using photoaffinity labeling, mass spectrometry, and NMR. Introduction of two tryptophan residues to the proposed binding site (I52W/L67W) mimics the effects of stimulator compounds, providing further evidence in support of our model. Additionally, drug response was reversibly decreased by covalently linking the coiled-coil domains. In summary, this work uncovers the binding site for sGC stimulatory compounds and provides mechanistic insight into drug response. Taken together, these findings lay the foundation for the development of new and improved pharmaceuticals targeted to sGC, as well as provide crucial insights into the function and regulation of this key therapeutic target.